Battery structure

ABSTRACT

A jacket for a multi-cell battery pack, the jacket having: outer walls defining a chamber for coolant fluid; a mid-wall partitioning the jacket into two regions; cell holders for holding the cells in place in the jacket so that each cell extends through the mid-wall; an inlet for coolant fluid on a first side of the mid-wall; and an outlet for coolant fluid on a second side of the mid-wall; the jacket defining a fluid path for the coolant fluid between the inlet and the outlet, the fluid path passing each cell of a set of the cells on both the first and second sides of the mid-wall.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and the benefit of United KingdomApplication No. GB 1303814.6, filed on Mar. 4, 2013. The entiredisclosure of the above application is expressly incorporated byreference in its entirety.

FIELD

This invention relates to battery structures.

BACKGROUND

High-capacity batteries are typically made from a number of individualcells which are bundled together physically, and interconnectedelectrically, to form a single battery pack. This arrangement has theadvantages of yielding a package that can have a high capacity whilstbeing made from mass-produced individual cells.

When a battery is being charged or discharged, heat can be generated inthe battery. If the battery is allowed to become too hot then itslifetime can be reduced, and at more extreme temperatures it may suffermajor damage. One way to limit overheating is to regulate the currentflow to prevent the temperature of the battery from exceeding a pre-setlimit. This can be practical in some operating conditions, but in othersituations this is less acceptable. For example, in a hybrid vehicle itis desirable to make the maximum use of any kinetic energy that isavailable for charging the battery. An alternative is to provide anarrangement for cooling the battery. For example, US 2012/0018238discloses a battery for a vehicle in which a cooling pack is installednear battery cells. US 2011/0048066 discloses a cooling jacket which hasa set of receptacles for receiving battery cells. Cooling fluidcirculates through the jacket.

Provided the cells of a battery pack are adequately connectedelectrically, they can be expected to heat up equally. Because of that,some benefit can be had from cooling the battery pack in any manner; butto maximise the benefit of cooling it is desirable for the cells to becooled as evenly as possible. Otherwise, performance may be limited byover-temperature in one of the cells when other cells might still be atan acceptable temperature.

If a battery pack is to be used in a vehicle, such as an automobile oraircraft, it is desirable for the battery to be as light as possible.Cooling arrangements that introduce excess weight are undesirable.

There is a need for a construction for a battery pack that can providefor uniform cooling without a substantial weight penalty.

SUMMARY

According to the present invention there is provided a jacket for amulti-cell battery pack, the jacket having: outer walls defining achamber for coolant fluid; a mid-wall partitioning the jacket and/or thechamber into two regions; cell holders for holding the cells in place inthe jacket so that each cell extends through the mid-wall; an inlet forcoolant fluid on a first side of the mid-wall; and an outlet for coolantfluid on a second side of the mid-wall; the jacket defining a fluid pathfor the coolant fluid between the inlet and the outlet, the fluid pathpassing each cell of a set of the cells on both the first and secondsides of the mid-wall.

The jacket may be configured such that, for each cell of the set, thepart of the fluid path from the inlet to a first passing of that cell isan analogue of the part of the fluid path from the second passing ofthat cell to the outlet. The first of those paths may be symmetricalwith the other about an axis or plane through the mid-wall. Preferablythe first of those paths is a mirror image of the second about themid-wall.

The cell holders may be tubes that extend through the intermediate wall.The tubes may be of circular cross-section.

The inlet and the outlet may be located at one end of the jacket. Theintermediate wall may seal one region of the jacket from the other withthe exception of one or more ports extending through the intermediatewall at the end of the jacket opposite the inlet and the outlet.

The set may consist of all the cells passed by the fluid path betweenthe inlet and the outlet.

The jacket may comprise a second inlet, a second outlet and a dividerextending in a direction transverse to the intermediate wall, thedivider dividing the interior of the jacket into two fluid zones suchthat a second fluid path through the jacket, separate from the firstfluid path, is defined between the second inlet and the second outlet.There could be multiple such dividers, together dividing the interior ofthe jacket into multiple fluid zones.

The cell holders may be arranged for holding cylindrical cells in ahexagonal close packed configuration. There may be spacing betweenadjacent cells. The or each fluid path may serve a set of cells whosewidth is two cells in the plane of the hexagonal close packing (i.e. thewidth of one repeat unit of the hexagonal close packing pattern). Eachcell may be elongate in a direction transvers to the mid-wall.

According to a second aspect of the invention there is provided a methodfor forming a sealed jacket for a multi-cell battery pack, the jackethaving a set of exterior walls defining the exterior of the jacket and aplurality of tubes, each tube running from an opening on the firstexterior wall to an opening on a second exterior wall opposite the firstexterior wall, the method comprising: assembling the walls and thetubes; and joining the walls and the tubes together by dip brazing.

The jacket of such a method may be a jacket as set out above.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described by way of example withreference to the accompanying drawings. In the drawings:

FIG. 1 shows a battery pack with cells fitted.

FIG. 2 shows the battery pack of FIG. 1 with the cells removed.

FIG. 3 shows an exploded view of the battery pack of FIG. 1 without thecells.

FIG. 4 illustrates the coolant path in the battery pack of FIG. 1.

FIG. 5 shows the battery pack of FIG. 1 as part of a batteryinstallation for a vehicle.

DETAILED DESCRIPTION

The battery pack of FIG. 1 comprises a set of individual electricalcells 1 which can be connected together electrically to allow them to becharged and discharged together. The cells are encased in a jacket. Thejacket is formed of sheets of metal which are joined together by adip-brazing process. The jacket serves the purpose of holding the cellstogether structurally and also of defining paths for coolant tocirculate through the battery pack so as to evenly cool the cells.

The structure of the jacket is best understood with reference to FIG. 3.The jacket has a front wall 10, a rear wall 11, a mid-wall 12, a bottomwall 13, a top wall 14, a left side wall 15, a right side wall 16, fourseparator walls 17-20 and a set of cell holders 25. Each of the walls ismade from a sheet of material. The sheets can be stamped/pressed intoshape to form the walls. The cell holders are tubular. They can be madefrom sheet material rolled into a loop and joined along the resultingseam to form a tube, by drawing or by any other suitable method. Thewalls and the cell holders can be formed of a plastics material or ametallic material such as aluminum. It is preferred that the cellholders are formed of a material having good thermal conductivity.

The periphery of the jacket is defined by the front, rear, top, bottomand side walls, which together form a box structure. The front and rearwalls have cut-outs 21. Each cut-out is shaped and sized so as to abutthe rim of a respective one of the cell holders 25. The front rims ofthe cell holders may abut the edges of the cut-outs in the front wall 10or extend beyond them away from the jacket's interior. The rear rims ofthe cell holders may abut the edges of the cut-outs in the rear wall 11or extend beyond them away from the jacket's interior. Once the outerwalls 10, 11, 13, 14, 15 and 16 are joined together around their edgesand to the cell holders the jacket forms a fluid-tight enclosure withthe exception of inlet and outlet ports 22, 23 and bleed ports 24. Thisis best seen in FIG. 2. The locations of the cell holders are fixed bythe locations of the cut-outs 21 in the front and rear walls 10, 11. Thecut-outs are located so that the cell holders are close together but nottouching each other, so that fluid in the jacket can flow between and incontact with the cell holders.

When the jacket is in use, cells 1 are inserted in the cell holders 25,as illustrated in FIG. 1. Each cell may be a sealed charge-storing unithaving electrical contacts on its exterior. Coolant circulating in thejacket can then cool the cells by conduction through the cell holders.Thermal paste is used to secure the cells and provide a conductive pathbetween the cells and cell holders.

Fluid circulation paths within the jacket are defined by the mid-wall 12and the separator walls 17-20. Like the front and rear walls, themid-wall has cut-outs 21 which are sized and shaped to receive the cellholders. The mid-wall is disposed mid-way between and parallel to thefront and rear walls, and is joined to the top, bottom and side wallsand to the cell holders mid-way along their lengths. In this way themid-wall divides the interior of the jacket into a front part and a rearpart. (See FIG. 4). Those parts are isolated from each other by themid-wall with the exception of slots 26. (See FIG. 3). Slots 26 extendthrough the mid-wall at its end opposite the inlet and outlet ports 22,23 and allow fluid communication through the mid-wall between the frontand rear parts. The separator walls are disposed between and parallel tothe side walls. Two of the separator walls 17, 18 are disposed betweenthe mid-wall and the front wall. They are joined to the mid-wall, thefront wall and the top and bottom walls. Two of the separator walls 19,20 are disposed between the mid-wall and the rear wall. They are joinedto the mid-wall, the rear wall and the top and bottom walls. In this waypairs of separators (17 and 19 on the one hand and 18 and 20 on theother) act together as dividers to divide the interior of the jacketinto three separate fluid zones 42, 43, 44. Within the jacket, fluidcannot communicate between zones 42, 43 and 44. Each of the slots 26 inthe mid-wall is located in a respective one of the zones so that fluidcan communicate through the slots between the front and rear parts ofeach zone.

The bottom wall 13 is at the opposite end of the jacket from slots 26.The bottom wall contains a set of inlet holes 22 and a set of outletholes 23. The inlet holes are located so that one inlet holecommunicates with each of the zones 42, 43, 44 between the mid-wall 12and the rear wall 11. The outlet holes are located so that one outlethole communicates with each of the zones 42, 43, 44 between the mid-wall12 and the front wall 10. This configuration enables fluid to circulatethrough the jacket along the paths illustrated in FIG. 4. In each of thezones 42, 43, 44 the fluid enters the jacket through one of the inlets22, passes up the rear part of the zone through a passageway defined bythe rear wall 11, the mid-wall 12 and whichever of the left wall 15, theright wall 16 and the rear separator walls 19, 20 bound the sides of therear part of the zone in question. At its upper end that passageway isbounded by top wall 14, but the fluid can pass through the respectiveone of the slots 26 in the mid-wall into the front part of the zone inquestion. Then the fluid can flow to one of the outlets 23 through apassageway defined by the front wall 10, the mid-wall 12 and whicheverof the left wall 15, the right wall 16 and the front separator walls 17,18 bound the sides of the front part of the zone in question. The fluidcan then exit the jacket through the respective outlet.

When cooling fluid is circulating through the jacket in the mannerdescribed above, each cell holder is exposed to fluid in both the rearpart of the jacket and the front part of the jacket. For example, cellholder 45 (FIG. 4) is exposed to fluid in the rear part of the jacket at46 and in the front part of the jacket at 47. Cell holder 48 is exposedto fluid in the rear part of the jacket at 49 and in the front part ofthe jacket at 50. The overall fluid path in one of the zones is shown at51 in FIG. 4. Partial fluid paths can be defined:

(a) in the rear part of the jacket from the inlet via any cell holder tothe cross-over slot 26; and

(b) in the front part of the jacket from the cross-over slot via thatcell holder to the outlet.

Each partial path serves a block of cells by passing and contacting thecell holders of those cells. Each block has an extent perpendicular tothe end walls of the battery pack. The partial fluid paths aresymmetrical about the mid-wall. As a result, when there is a substantialdifference between the inlet coolant temperature and the celltemperature throughout the jacket, it can be expected that the averageof the temperature of the cooling fluid to which a cell holder isexposed in the rear part of the jacket and the temperature of thecooling fluid to which a cell holder is exposed in the front part of thejacket is substantially the same for all the cell holders. Thetemperature of the coolant when it reaches a point at which it passes acell will depend on the inlet temperature of the coolant and the energytransfer to the coolant between the inlet and the point in question. Asan example, if the inlet coolant temperature is 30° C. and the outletcoolant temperature is 50° C. the cell holder 45 might be exposed tocoolant at 32° C. at point 46 and at 48° C. at point 47 (average coolanttemperature=(32° C.+48° C.)/2=40° C.) whereas cell holder 48 might beexposed to coolant at 38° C. at point 49 and at 42° C. at point 50(average coolant temperature=(38° C.+42° C.)/2=40° C.). Since thermalconductivity within a cell can be expected to be good, arranging thecirculation paths in this way allows all the cells to be maintained at auniform temperature irrespective of their location within the jacket.

In the jacket of the figures, each of the zones 42, 43, 44 has a singleslot 26. There could be multiple openings for communication between theparts of a zone. Those openings could be located exclusively at the endsof the zone opposite the inlet and the outlet.

The inlet and outlet ports 22, 23 can be connected to a manifold 27 andvia that to a coolant circuit. The coolant circuit can include a pumpfor forcing coolant to circulate in the circuit and a heat exchanger forcooling the coolant, for instance by releasing heat to ambient air. Thecoolant could circulate by convection, in which case no pump would berequired.

To permit the jacket to be filled with coolant when the battery iscommissioned, bleed holes 24 for air are provided at the top of thejacket. The bleed holes can be connected to a bleed pipe 28 which allowsmultiple zones to be bled simultaneously. The bleed holes and/or thebleed pipe can be sealed once the battery is in use, or the bleed pipemay be used as a running bleed.

As described above, the walls of the jacket are joined to each other andto the cell holders in a fluid-tight manner around their peripheries.This could be done by a number of methods, for example by welding theelements of the jacket together. The jacket could be moulded or cast asa single unit. However, it has been found particularly efficient to formthe walls and the cell holders individually and then to join themtogether by dip brazing. In dip brazing the parts to be joined areassembled and braze is applied at the intended joins. Then the assemblyis immersed in a hot bath. The hot bath melts the braze and the brazeflows by capillary action along the interfaces between the parts. Theassembly is then removed from the bath and the braze cools, setting thejoints between the parts. Dip brazing can permit the jacket to beassembled efficiently and so as to be reliably fluid-tight whilstpermitting the walls of the jacket and especially of the cell holders tobe made of relatively thin material. The walls of the jacket can befitted with tabs to allow them to be clipped together prior to brazing.

Once the jacket has been assembled, the cells can be inserted in thecell holders. As well as providing cooling for the cells, the jacket canserve as the structural support for the cells. The jacket can be thesole means of holding the cells in the jacket in place relative to eachother. The cell holders can be sized so as to snugly receive the cells;then no additional fixings may be needed to hold the in place. Thermalpaste is used to improve thermal conductivity. The cell holders permitthe ends of the cells to be exposed once the cells are inserted in thecell holders. The electrical terminals 2 of the cells can be located atthe ends of the cells. The cells can then be connected electricallyafter they have been inserted in the cell holders. FIG. 5 shows abattery installation for use in a vehicle. In the battery installationsix jackets as described above, with their cells, are attached togetherphysically. The cells can be interconnected electrically as required,for example by connecting the cells within a jacket to positive andnegative terminations on that jacket, and then connecting he positiveterminals of the jackets together with a first busbar, and connectingthe negative terminals of the jackets together with a second busbar. Thecells of a jacket could be connected in series and/or parallel. To makeit easier to interconnect the cells, some could present their electricalterminals on one side of the jacket and some on the other. The manifolds27 of each jacket can be connected to a common coolant supply/returnpipe 29 as shown in FIG. 5.

In the jacket described above, the cell holders take the form of tubesextending from openings on one exterior wall to the jacket tocorresponding openings on the other wall of the jacket. The openingsmatch in shape and size the interior profile of the tubes. Otherarrangements are possible. For example, the cell holders could bethreaded or provided with clips to hold the cells in place, or the cellsthemselves could be attached integrally to the front, rear andmid-walls, in which case the cells would be located by the openings inthe walls to which the cells attach, and those openings could beconsidered as cell holders.

The jacket shown in the figures is configured for accommodating cellsthat are circularly cylindrical. The cell holders 25 are arranged in ahexagonally close packed manner so as to achieve a high density of cellsin the battery pack, albeit that each cell holder is spaced slightlyfrom its neighbours so as to permit coolant to flow between them. Eachzone 42, 43, 44 serves a column of cells that extends parallel to theprimary directions of flow in the fluid paths. Each column has an extentof two cells in the plane of the close packing. By dividing the batterypack into narrow columns in this way, the possibility of non-uniformcooling of some of the cells due to differences in flow patterns acrossthe plane of close packing can be reduced. The separators 17-20 arelocated between cells, and extend out of the plane of the close packing.To permit the separators to fit between the close-packed cells theseparators are corrugated.

In the jacket described above, the walls are arranged in a generallyperpendicular fashion. The walls could be arranged obliquely. The wallsneed not be generally flat. In the jacket described above the mid-wall12 runs the full width of the jacket and the each of the separators17-20 runs part-way across the depth of the jacket. Alternatively, theseparators could run the full depth of the jacket and the mid-wall couldbe formed in multiple parts that run between the separators.

The applicant hereby discloses in isolation each individual featuredescribed herein and any combination of two or more such features, tothe extent that such features or combinations are capable of beingcarried out based on the present specification as a whole in the lightof the common general knowledge of a person skilled in the art,irrespective of whether such features or combinations of features solveany problems disclosed herein, and without limitation to the scope ofthe claims. The applicant indicates that aspects of the presentinvention may consist of any such individual feature or combination offeatures. In view of the foregoing description it will be evident to aperson skilled in the art that various modifications may be made withinthe scope of the invention.

1. A jacket for a multi-cell battery pack, the jacket having: outerwalls defining a chamber for coolant fluid; a mid-wall partitioning thejacket into two regions; cell holders for holding the cells in place inthe jacket so that each cell extends through the mid-wall; an inlet forcoolant fluid on a first side of the mid-wall; and an outlet for coolantfluid on a second side of the mid-wall; the jacket defining a fluid pathfor the coolant fluid between the inlet and the outlet, the fluid pathpassing each cell of a set of the cells on both the first and secondsides of the mid-wall.
 2. A jacket as claimed in claim 1, the jacketbeing configured such that, for each cell of the set, the part of thefluid path from the inlet to a first passing of that cell is an analogueof the part of the fluid path from the second passing of that cell tothe outlet.
 3. A jacket as claimed in claim 1, wherein the cell holdersare tubes that extend through the intermediate wall.
 4. A jacket asclaimed in claim 1, wherein the inlet and the outlet are located at oneend of the jacket and the intermediate wall seals one region of thejacket from the other with the exception of one or more ports extendingthrough the intermediate wall at the end of the jacket opposite theinlet and the outlet.
 5. A jacket as claimed in claim 1, wherein the setconsists of all the cells passed by the fluid path between the inlet andthe outlet.
 6. A jacket as claimed in claim 1, wherein the jacketcomprises a second inlet, a second outlet and a divider extending in adirection transverse to the intermediate wall, the divider dividing theinterior of the jacket into two fluid zones such that a second fluidpath through the jacket, separate from the first fluid path, is definedbetween the second inlet and the second outlet.
 7. A jacket as claimedin claim 1, wherein the cell holders are arranged for holdingcylindrical cells in a hexagonal close packed configuration with spacingbetween adjacent cells.
 8. A jacket as claimed in claim 7, wherein theor each fluid path serves a set of cells whose width is two cells in theplane of the hexagonal close packing.
 9. A method for forming a sealedjacket for a multi-cell battery pack, the jacket having a set ofexterior walls defining the exterior of the jacket and a plurality oftubes, each tube running from an opening on the first exterior wall toan opening on a second exterior wall opposite the first exterior wall,the method comprising: assembling the walls and the tubes; and joiningthe walls and the tubes together by dip brazing.
 10. A method as claimedin claim 9, wherein the jacket is a jacket as claimed in any of claim 1.